Akt1, also known as protein kinase B? (PKB?), is the founding member of a protein kinase family composed of three members, Akt1, Akt2 and Akt3. Akt family members regulate a diverse array of cellular functions including apoptosis, cellular proliferation, differentiation and intermediary metabolism and they appear to play a very important role in human cancer. Using single Akt knockout mice, and mice lacking combinations of two or all three isoforms of Akt in T cells, we have shown that specific combinations of Akt isoforms regulate multiple steps in thymopoiesis and are required for the physiological function of fully differentiated mature T cells. In other studies, we have shown that mice with a combined ablation of Akt1 and Akt2, but not other combinations of Akt isoforms in T cells, lack detectable regulatory T cells in both the thymus and the spleen and develop a severe autoimmune syndrome. Finally, macrophages from Akt2, but not Akt1 or Akt3 knockout mice exhibit a defect in the induction of COX2 and TNF-? in response to LPS. The experiments in this proposal will utilize molecular biology, tissue culture and genetic strategies to address the role of different Akt isoforms in thymocyte differentiation and T cell function, with special emphasis on the regulatory T cells. These experiments will generate basic information regarding the function of the immune system. In addition, they are expected to generate information, which will allow us to make predictions regarding the potential toxicity of Akt inhibitors under development.